fix test

Author: yufeih

src/Docfx.Build/TableOfContents/TocHelper.cs

@@ -82,7 +82,7 @@ public static TocItemViewModel LoadSingleToc(string file)
         }
         catch (Exception e)
         {
-            var message = $"{file} is not a valid TOC File: {e.Message}";
+            var message = $"{file} is not a valid TOC File: {e}";
             Logger.LogError(message, code: ErrorCodes.Toc.InvalidTocFile);
             throw new DocumentException(message, e);
         }

test/Docfx.Build.Tests/TocDocumentProcessorTest.cs

@@ -761,7 +761,7 @@ public void LoadBadTocYamlFileShouldGiveLineNumber()
       href: x2.md";
         var toc = _fileCreator.CreateFile(content, FileType.YamlToc);
         var ex = Assert.Throws<DocumentException>(() => TocHelper.LoadSingleToc(toc));
-        Assert.Equal("toc.yml is not a valid TOC File: toc.yml is not a valid TOC file, detail: (Line: 3, Col: 10, Idx: 22) - (Line: 3, Col: 10, Idx: 22): While scanning a plain scalar value, found invalid mapping..", ex.Message);
+        Assert.Equal("toc.yml is not a valid TOC File: (Line: 3, Col: 10, Idx: 22) - (Line: 3, Col: 10, Idx: 22): While scanning a plain scalar value, found invalid mapping.", ex.Message);
     }
 
     [Fact]